High resolution control system

ABSTRACT

A high resolution control system for aircraft, such as a helicopter, in which a mechanical control system for translating motion from a pilot operated input member to a remotely located output member has a mechanical connection between the input member and the output member including a walking beam located adjacent the output member and means for providing a second input supplied directly to said walking beam in response to an electrical system producing an error signal by comparing a first signal generated in response to displacement of the input member with a feedback signal generated in response to displacement of the walking beam. The invention described herein was made in the course of or under a contract or subcontract thereunder with the Department of the Navy.

United States Patent inventors Appl. No. Filed Patented Assignee HIGHRESOLUTION CONTROL SYSTEM 6 Claims, 2 Drawing Figs.

US. Cl

Int. Cl B64c 13/04 Field of Search 244/83, 84,

References Cited UNITED STATES PATENTS 1/1966 Edenborough 244/ 83X3,396,597 8/1968 Dean 244/83X Primary ExaminerMilton Buchler AssistantExaminer-Carl A. Rutledge Attorneys-Maurice B. Tasker and Vernon F.Hauschild ABSTRACT: A high resolution control system for aircraft, suchas a helicopter, in which a mechanical control system for translatingmotion from a pilot operated input member to a remotely located outputmember has a mechanical connection between the input member and theoutput member including a walking beam located adjacent the outputmember and means for providing a second input supplied directly to saidwalking beam in response to an electrical system producing an errorsignal by comparing a first signal generated in response to displacementof the input member with a feedback signal generated in response todisplacement of the walking beam.

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1 HIGH RESOLUTION CONTROL SYSTEM The invention described herein was madein the course of or under a contract or subcontract thereunder with theDepartment of the Navy.

BACKGROUND OF THE INVENTION I-Ieretofore, control systems for moving anoutput member, such as improved blade resolution control member of ahelicopter tail rotor, comprised a manually operable member located inthe pilots compartment driving, by means of cables and linkages, ahydraulic servoactuator located adjacent the tail rotor which positionsthe output member. Particularly in helicopter tail rotor control systemsthere is a large amount of lost motion, or backlash, due to the longmechanical linkage between the input and output members. Further, thelong tail cone of a helicopter of the type utilizing an antitorque tailrotor flexes in flight and is also subject to thermal expansion andcontraction, all of which results in a low relative correspondencebetween input and output inthe control system.

SUMMARY OF THE INVENTION tion control system which is basicallymechanical, utilizing electrically sensed corrections which are applied,together with the mechanical controls, through improved differentialmechanism located adjacent the tail rotor.

A still further object of our invention is to provide improved mechanismfor introducing corrective input signals to the blade pitch controlservomotor including a differential linkage.

Other objects and advantages of our invention will become evident fromthe following detailed description of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic view of ourimproved high resolution control system as applied to the yaw control ofa helicopter; and

FIG. 2 is a longitudinal sectional view of a spring loaded centeringdevice used in the system.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, pilotoperated pedals l drive the input of a secondary hydraulic servo 12. Theautomatic flight control system 13 also drives the input of secondaryhydraulic servo 12. The output shaft of servo 12 is coupled with amixing unit 14, the construction of which is shown and fully describedin the Dean et al. US Pat. No. 3,199,601. As is well known in thehelicopter art, changes in the position of the collective pitch controlstick 15 produce changes in the main rotor pitch which necessitatesvariation in the power output of the engine in order to maintainconstant rotor speed. Resulting variations in engine torque arecompensated for by introducing motion of the collective stick into theyaw channel to produce a corresponding change in tail rotor pitch. Thismixing unit 14 is essentially a mechanical summing device.

The output of unit 14 is coupled through mechanical linkage 16, whichextends from unit 14 adjacent the main rotor along the entire length ofthe tail cone, to a differential linkage, generally indicated at A,located adjacent the tail rotor. Difierential linkage A includes awalking beam 18 having trunnions 20 which are pivotally mounted in thespaced arms 22 of a secondary input link 24, thus providing a pivotalsupport for the walking beam about axis A-A. Link 24 is pivotallymounted at 25 on fixed aircraft structure at the endsof arms 22 toprovide for pivotal movement of link 24 about axis B-B.

Mechanical linkage 16 has a rear terminal link 26 which is pivotallyconnected at 28 to the lower bifurcated end of walking beam 18, thusproviding mechanical input from the pilot's pedals to the difierentiallinkage. The walking beam is also bifurcated at its up eie'naiafiervearmnarmd 30 which extends both fore and aft beyond the walkingbeam and has an intermediate hub 31 which is pivoted at 32 in the upperfurcations of beam 18.

The aft portion 34 of rod 30 is connected directly to the tail rotorservo 35. The forward portion 36 is connected to the operating arm 38 ofan electrical yaw control system output displacement sensor 40. At theother end of the mechanical linkage an electrical yaw control systeminput sensor 42 is operatively connected to linkage 16 adjacent to andat the output of the mechanical mixer 14. The outputs 44 and 46 of thetwo electrical sensors are connected to an electrical comparator(differential amplifier) 48, the output signal 50 of which controls avalve 52 of an electrohydraulic actuator 54 that is pinned to aircraftstructure at one end. The electrohydraulic actuator piston 56 ofactuator 54 is pivotally connected at 58 to the bifurcated upper end ofsecondary input link 24.

A centering spring 59, FIG. 2, is provided in a cylinder 60 which ispivotally connected by a rod 62 to fixed aircraft structure at 64. Anactuating rod 66, loaded by spring 59, is pivoted at 68 to the lower endof walking beam 18 at a point just above a pivot 28 for input rod 26.The spring within the cylinder 60 is preset to have a zero load at aposition of the rod 66 which corresponds to a selected positive pitchsetting of the tail rotor blades to automatically adjust the blade pitchand provide directional control of the helicopter in the event that thelinkage between the controls after the input sensor 42 and walking beam18 is severed at any point. This centering spring and its function arefully disclosed and claimed in a copending application of James C. Dean,Ser. No. 819,578, filed Apr. :28, 1969, and assigned to the assignee ofthis application.

In the operation of our invention, movements of the pilots pedals 10 arecoupled through secondary servo 12, mechanical mixer 14, linkage l6 andwalking beam l8'to shaft 34 which is directly' connected to the input ofthe primary servo of the tail rotor. As rod 26, which is the terminalmember of linkage 16, moves the walking beam about its axis A-A springbiased rod 66 is also moved to vary the compression of the spring incylinder 60. This movement of rod 66 has no effect, however, on thenormal operation of the control system through linkage 16 except thatthe spring beneficially takes out the backlash in the linkage due toplay in the bearings and pivots of the linkage. The spring does not,however, bias out play at the springs neutral position where force isnot available to push the system to either side. Also when passingthrough the neutral position the play bias position changes from oneextreme of the play to the other, thus; producing a control error. Thespring also does not. compensatefor induced control errors due tofuselage bending or fuselage thermal expansion and contraction. Thus thecentering spring alone is not capable of producing a high resolutioncontrol system.

Yaw control system input sensor 42 generates an output voltage which isproportional to the displacement .of the mechanical mixer output.Likewise the tail rotor servo output sensor 40 generates a voltageoutput which is proportional to the actual mechanical movement of thetail rotor servo input control rod 34. By comparing these voltages incomparator-48 a resultant voltage signal is obtained which, when appliedto secondary input link actuator 54, will cause secondary input.

link 24 to apply the required correcting motion to walking beam 18 androd 34 to produce perfect resolution in the control system under allconditions of flight.

If the control linkage 16 should be severed at any point along itslength, .the centering spring 59 will move the tail rotor pitch to afixed trim position and the pivot for the walking beam 18 at its lowerend becomes a fixed pivot about axis C-C. Input motions of link 24 thenpivot walking beam-18 about axis CC and position the primary servo,thereby providing yaw control of the helicopter. The authority ofsecondary input link 24 is increased above normal system operation bythus locating the fixed pivot point 28 for the walking beam nearer pivotfor the latter on link 24. This amounts to about 20 percent increase inthe capability of input link 24, in the mechanism illustrated, whichgives the pilot ample control to fly the aircraft safely back to base.

it will be evident that by this invention we have made it possible toreduce the control error between the mechanical mixer and the primarycontrol servo and thereby materially improve aircraft performance. Alsowe have made it possible to compensate for induced control inputs causedby fuselage bending and thermal expansion and contraction of thefuselage.

We claim:

1. A high resolution tail rotor pitch control system for helicoptersincluding in combination a first movable input member, a movable outputmember, means responsive to movement of said input member for providinga first electrical signal, means responsive to movementpf said outputmember for providing a feedback signal, means for comparing said firstand feedback signals to provide an error signal, and means responsive tomovement of said first movable member and to the error signal forpositioning said output member including a differential linkagemechanism, said mechanism including a second input link responsive tosaid error signal pivoted on fixed aircraft structure, and a walkingbeam pivoted intermediate its length on said second input member andoperatively connected at points spaced from its pivot on said secondinput link with both said first movable input member and said outputmember.

2. A high resolution tail rotor pitch control system including a pilotoperated control member, a tail rotor pitch control servo, a mechanicalconnection between said member and said servo including a walking beamhaving a pivotal support adjacent said servo and having an operatingconnection with said servo on one side and an operating connection withsaid member on the other side of its pivot, an electrical input sensorresponsive to movements of said member an electrical out- ;put sensorresponsive to movements of said walking beam, means for comparing theelectrical outputs of said sensors to obtain an error signal, and meansresponsive to said error signal for providing a corrective movement ofsaid walking bam to produce a high degree of resolution between themovements of said member and said servo.

3. A high resolution tail rotor pitch control system including a pilotoperated member, a tail rotor pitch control servo, a mechanicalconnection between said member and said servo including a walking beampivoted adjacent said servo and having an operating connection with saidservo on one side and an operating connection with said member on theother side of its pivot, an input sensor responsive to movements of saidmember having an electrical output, an output sensor responsive tomovements of said walking beam having an electrical output, means forcomparing the electrical outputs of said sensors to obtain an errorsignal, a secondary input arm pivoted on fixed aircraft structure havingan operative connection with said walking beam, and actuating means forsaid input arm energized by said error signal providing a correctivemovement of said walking beam to produce a high degree of resolutionbetween the movements of said member and said servo.

4. The control system of claim 3 in which the walking beam is pivotallymounted intermediate its ends on the secondary input arm.

5. A high resolution tail rotor pitch control system for a helicopterincluding a pilot operated member, an input sensor operatively connectedto said member and having an electrical output proportional to movementof said member, a tail rotor pitch control servo, an output sensoroperatively connected to said servo and having an electrical outputproportional to movement of said servo, input means providing amechanical connection between said member and said servo including adifferential linkage located adjacent said servo, said linkage includinga walking beam and a second input member ivoted at one end on fixedaircraft structure, said walking eam being pivoted intermediate its endson said second input member at a point spaced from the pivotal supportof the latter, a differential amplifier receiving the electrical outputfrom both said sensors and producing therefrom an error signal, and anextensible actuator receiving said error signal and having an operativeconnection with the free end of said second input member.

6. The control system of claim 5 in which said input means includes alinkage having a pivotal connection to one end of said walking beamremote from the pivotal support for the latter, a spring biasedcentering mechanism including a cylinder pivotally supported on fixedaircraft structure and a spring biased cylinder rod pivotally connectedto said walking beam at a point somewhat closer to the pivot of thelatter than the pivot of said linkage on said beam.

1. A high resolution tail rotor pitch control system for helicoptersincluding in combination a first movable input member, a movable outputmember, means responsive to movement of said input member for providinga first electrical signal, means responsive to movement of said outputmember for providing a feedback signal, means for comparing said firstand feedback signals to provide an error signal, and means responsive tomovement of said first movable member and to the error signal forpositioning said output member including a differential linkagemechanism, said mechanism including a second input link responsive tosaid error signal pivoted on fixed aircraft structure, and a walkingbeam pivoted intermediate its length on said second input member andoperatively connected at points spaced from its pivot on said secondinput link with both said first movable input member and said outputmember.
 2. A high resolution tail rotor pitch control system including apilot operated control member, a tail rotor pitch control servo, amechanical connection between said member and said servo including awalking beam having a pivotal support adjacent said servo and having anoperating connection with said servo on one side and an operatingconnection with said member on the other side of its pivot, anelectrical input sensor responsive to movements of said member anelectrical output sensor responsive to movements of said walking beam,means for comparing the electrical outputs of said sensors to obtain anerror signal, and means responsive to said error signal for providing acorrective movement of said walking beam to produce a high degree ofresolution between the movements of said member and said servo.
 3. Ahigh resolution tail rotor pitch control system including a pilotoperated member, a tail rotor pitch control servo, a mechanicalconnection between said member and said servo including a walking beampivoted adjacent said servo and having an operating connection with saidservo on one side and an operatiNg connection with said member on theother side of its pivot, an input sensor responsive to movements of saidmember having an electrical output, an output sensor responsive tomovements of said walking beam having an electrical output, means forcomparing the electrical outputs of said sensors to obtain an errorsignal, a secondary input arm pivoted on fixed aircraft structure havingan operative connection with said walking beam, and actuating means forsaid input arm energized by said error signal providing a correctivemovement of said walking beam to produce a high degree of resolutionbetween the movements of said member and said servo.
 4. The controlsystem of claim 3 in which the walking beam is pivotally mountedintermediate its ends on the secondary input arm.
 5. A high resolutiontail rotor pitch control system for a helicopter including a pilotoperated member, an input sensor operatively connected to said memberand having an electrical output proportional to movement of said member,a tail rotor pitch control servo, an output sensor operatively connectedto said servo and having an electrical output proportional to movementof said servo, input means providing a mechanical connection betweensaid member and said servo including a differential linkage locatedadjacent said servo, said linkage including a walking beam and a secondinput member pivoted at one end on fixed aircraft structure, saidwalking beam being pivoted intermediate its ends on said second inputmember at a point spaced from the pivotal support of the latter, adifferential amplifier receiving the electrical output from both saidsensors and producing therefrom an error signal, and an extensibleactuator receiving said error signal and having an operative connectionwith the free end of said second input member.
 6. The control system ofclaim 5 in which said input means includes a linkage having a pivotalconnection to one end of said walking beam remote from the pivotalsupport for the latter, a spring biased centering mechanism including acylinder pivotally supported on fixed aircraft structure and a springbiased cylinder rod pivotally connected to said walking beam at a pointsomewhat closer to the pivot of the latter than the pivot of saidlinkage on said beam.